1. Field of Invention
This invention relates to aqueous fluorocarbon polymer coating compositions and articles coated therewith and more particularly to such compositions and metallic articles coated therewith having improved post oil adhesion.
2. Prior Art
In recent years, the use of fluorocarbon polymer coatings as non-stick finishes for metal substrates, particularly for cookware, has become widespread. The physical nature of fluorocarbon polymers makes it difficult to adhere them to metallic substrates sufficiently well to prevent coatings of the polymers from blistering and peeling during use. This is especially true for polytetrafluoroethylene.
Adhesion of the coatings has been improved by the addition of a water-soluble alkali metal silicate and colloidal silica to the fluorocarbon polymer coating composition as described in U.S. Pat. No. 2,825,664, issued Mar. 4, 1958 to James R. Huntsberger. In U.S. patent application Ser. No. 348,315 filed Apr. 5, 1973, in the name of Edward J. Welch and assigned to the assignee of this application, now abandoned in favor of a continuation-in-part application Ser. No. 405,798, filed Oct. 12, 1973, adhesion was improved by adding colloidal silica stabilized with sodium ions to the fluorocarbon polymer coating composition.
While the compositions described in the aforesaid references do improve adhesion to unprimed metal substrates, there are some end-use applications where improved post oil adhesion (i.e., resistance to hot oil) is desirable. In cookware, improved post oil adhesion is desirable in such articles as fry pans, meat grills, sauce pans or other articles where fats and oils are in contact with the fluorocarbon polymer coating.